The environmental chemical, 4-Vinylcyclohexene (VCH) is produced in the manufacture of rubber tires, flame retardants, insecticides, plasticizers, and antioxidants. Dosing (30 d) with the diepoxide metabolite, 4- vinylcyclohexene diepoxide (VCD) destroys the majority of small pre-antral (primordial) follicles in the ovaries of mice and rats. Females are born with a finite number of primordial follicles that cannot be regenerated; thus, chemicals that destroy oocytes contained in these follicles can produce premature ovarian failure. Exposure of women to known ovotoxicants such as cigarette smoke and chemotherapeutic agents has been associated with early menopause, thus, potential exposure to other ovotoxic chemicals in the industrial setting is of concern. Previous studies with VCD (80mg/kg) in rats showed that destruction of small follicles requires daily dosing (10 days), is via physiological cell death (apoptosis), and is accompanied by altered expression of genes associated with apoptosis (bax), oxidative stress (superoxide dismutase, and detoxification (epoxide hydrolase). The studies, proposed here will characterize the role of oxidative stress and follicular metabolism in VCD-induced apoptosis. The experimental approach will involve exploiting the shift in responsiveness to VCD dosing we have observed in small follicles from a protective effect (1 dose), to an apoptotic effect (10 and 15 daily doses). Additionally, these studies will use the isolated small follicle system we have developed in conjunction with confocal microscopy to localize events within specific cells. The hypothesis to be tested is that: VCD initiates an oxidative stress response in small pre-antral follicles that is altered after repeated dosing to trigger the onset of bax- mediated apoptosis. The Specific Aims are 1) to characterize the oxidative stress response in bax-mediated apoptosis, 2) to relate VCD metabolism with oxidative stress in small follicles, and 3) to evaluate the stress-activated pathway to apoptosis. The studies will use an integrated morphological, biochemical and molecular approach to provide a greater understanding of the mechanisms of ovotoxicity caused by occupational, epoxides. The results of these studies will provide greater insight as to the impact of exposure to ovotoxic environmental chemicals on reproductive health in women.